As cell-phones and information terminals have been advanced, image display apparatuses become smaller and finer. On the other hand, as new value-added image display apparatuses, attention has been drawn to image display apparatuses allowing the observer to view different images depending on the observing point, namely image display apparatuses making different images visible at multiple observing points, and to three-dimensional image display apparatuses presenting different images as parallax images and allowing the observer to view a three-dimensional image.
Techniques of providing different images to multiple observing points consist of merging image data for different observing points and displaying them on a display panel, separating the displayed composite image by an optical separation means such as a lens and a barrier having slits (a screen), and providing the images to individual observing points. In principle, images are separated by an optical means such as a barrier having slits and a lens so as to limit each image to a direction of observing point. A parallax barrier consisting of a barrier having many slits in a stripe pattern or a lenticular lens consisting of an array of cylindrical lenses having lens effect in one directional is generally used as the image separation means.
A three-dimensional image display apparatus having an optical image separation means is suitable for installing in terminal devices such as cell-phones because it does not require wearing special glasses and eliminates annoyance of wearing glasses. Cell-phones carrying a three-dimensional display apparatus consisting of a liquid crystal panel and a parallax barrier are already commercialized (for example, see NIKKEI Electronics, Jan. 6, 2003, No. 838 (Non-Patent Literature 1, hereafter), pp 26-27).
The above technology, namely a three-dimensional image display apparatus providing different images to multiple observing points using an optical separation means sometimes causes the observer to see a dark boundary between images when he/she shifts the observing point and the observed image is switched. This phenomenon occurs when a non-display region between pixels for different observing points (a shielding part generally called a black matrix in a liquid crystal panel) is viewed. This phenomenon accompanying shift of the observing point of the observer does not occur with a general three-dimensional display apparatus without an optical separation means. Therefore, the observer experiences discomfort or senses deterioration in the display quality from the above phenomenon occurring with a multi-viewpoint three-dimensional display apparatus or three-dimensional display apparatus with an optical separation means.
This is a phenomenon generally called 3D moire. The 3D moire is a periodically appearing uneven luminance (sometimes referred to as uneven color) caused by displaying different images in different angular directions. Furthermore, the 3D moire is luminance angular fluctuation and large luminance angular fluctuation has adverse effect on three-dimensional observation.
In order to ameliorate the above problem caused by an optical separation means and shielding part, three-dimensional image display apparatuses in which the shape and geometry of pixel electrodes and shielding part of the display panel is designed to reduce deterioration in the display quality have been proposed (for example, Unexamined Japanese Patent Application KOKAI Publication Nos. 2005-208567 (Patent Literature 1, hereafter) and H10-186294 (Patent Literature 2, hereafter)).
FIG. 37 is a plane view showing the display panel of the display apparatus disclosed in Patent Literature 1. In the display apparatus disclosed in the Patent Literature 1, at any point in the horizontal direction 1012, the shielding part (the wire 1070 and shielding part 1076) and aperture are provided nearly at a fixed ratio in a cross-section of the display panel in the vertical direction 1011 perpendicular to the direction of the array of cylindrical lenses 1003a. 
Therefore, even if the observer shifts his/her observing point in the horizontal direction 1012, which is the image separation direction, so as to change the observing direction, the shielding part viewed is nearly at the fixed ratio. In other words, it does not happen to the observer to see only the shielding part in a specific direction or to see a darker display. Then, deterioration in the display quality caused by the shielding region is prevented.
FIG. 38 is a schematic illustration showing pixels of the three-dimensional display apparatus disclosed in the Patent Literature 2. FIG. 38 (A) is a plane view showing the pixel arrangement of the three-dimensional display apparatus disclosed in the Patent Literature 2 and FIG. 38 (B) is an enlarged view of a pixel thereof. In the three-dimensional display apparatus disclosed in the Patent Literature 2, the total vertical dimension of horizontally adjacent pixels is constant at any position in the horizontal direction in the overlapping region. The total dimension is equal to the vertical dimension of a rectangular region B. Therefore, horizontally continuous and substantially uniform luminance is provided and substantially constant luminance is maintained all over.
Therefore, when the same image is output to adjacent columns of pixels, constant luminance is maintained even if the observer's eye crosses a boundary between apertures.
For easier understanding, a typical prior art pixel structure will be described hereafter with reference to the drawings. FIG. 36 is an illustration schematically showing a prior art pixel structure disclosed in the Patent Literature 1 and 2.
For simplified explanation, a display unit 4 consisting of a pair of a right-eye pixel 4R and a left-eye pixel 4L is shown. The aperture of each pixel has an isosceles trapezoid shape. When the focus is on one of the minimum unit pixels (the right-eye pixel 4R or the left-eye pixel 4L) constituting the display unit 4, it is referred to as “a sub-pixel” without particular distinction.
The display unit 4 comprises at least the right-eye pixel 4R and left-eye pixel 4L as two sub-pixels adjacent to each other in the X-axis direction. The three-dimensional image display apparatus comprises a cylindrical lens 1003a as an optical means for separating light emerging from the apertures of sub-pixels into separated images in the X-axis direction.
Here, the image separation direction is defined as the X-axis direction and the direction perpendicular thereto is defined as the Y-axis direction. Furthermore, the term “vertical aperture” refers to the width of an aperture in the direction perpendicular to the image separation direction (which corresponds to the Y-axis in the case of FIG. 37). Of the bases of the trapezoid of a sub-pixel aperture, the smaller base is referred to as the upper base and the larger base is referred to as the lower base.
The aperture of the right-eye pixel 4R and the aperture of the left-eye pixel 4L are provided next to each other in the X-axis direction. There is a region on their border where these apertures overlap with each other in the Y-axis direction. The region where these apertures overlap with each other is termed “the overlapping region” and the width of such a region in the X-axis direction is defined as an overlapping region width Xct1. On the other hand, a region in the center of the aperture where the aperture of the right-eye pixel 4R and the aperture of the left-eye pixel 4L do not overlap with each other is termed “the non-overlapping region” and the width of such a region in the X-axis direction is defined as a non-overlapping region width X1. The pitch Xdot of sub-pixels in the X-axis direction is equal to the sum of the overlapping region width Xct1 and non-overlapping region width X1.
The aperture of a sub-pixel is in the shape of an isosceles trapezoid symmetric about a line b-b′ parallel to the Y-axis and passing through the center of the sub-pixel and having upper and lower bases parallel to the X-axis. A shielding line having a finite width W is provided on the oblique sides of the trapezoid. The oblique side makes an angle θ with respect to the Y-axis. The shielding line is termed “the oblique wire.”
Points A and A′ are the vertexes of the lower bases of the trapezoidal apertures of the sub-pixels. Points B and B′ are the vertexes of the upper bases of the trapezoidal apertures of the sub-pixels. The points A and A′ and points B and B′ are inflexion points where the vertical aperture width of a sub-pixel starts to change in the X-axis direction. A point C is a point where a line parallel to the Y-axis and passing through the point B and the lower base of the trapezoidal aperture intersect and so is a point C′ with regard to the point B′.
The line connecting the points A and B and the line connecting the points A′ and B′ are parallel to each other. Then, the total of the vertical aperture widths of the right-eye pixel 4R and left-eye pixel 4L in the overlapping region is always constant in the X-axis direction. Furthermore, the points A and B′ and points A′ and B are situated on the same line parallel to the Y-axis, respectively, so that the vertical aperture width in the non-overlapping region and the total of the vertical aperture widths of the apertures of the right-eye pixel 4R and left-eye pixel 4L in the overlapping regions are equal. In this way, the vertical aperture width is constant from the overlapping region to the non-overlapping region and always constant throughout a sub-pixel in the X-axis direction.
The display unit 4 has an oblique wire making an angle θ with respect to the Y-axis and having a display wire width W. The sides of the oblique wire are connected to the lower bases of the trapezoidal apertures at the points A and A′ and connected to the upper bases of the trapezoidal apertures at the points B and B′. The oblique wire is connected to a shielding part at the trapezoid upper base. This shielding part has a width Y2 in the Y-axis direction and provides a region where, for example, transistors and capacitors for operating the sub-pixel are formed.
The total of the vertical aperture widths of adjacent sub-pixels is constant in the X-axis direction. Therefore, assuming that lights equal in luminance are emitted from the aperture region in the overlapping region and the aperture region in the non-overlapping region, the luminance is maintained constant at observation positions parallel to the X-axis. Then, there is no luminance angular fluctuation, in other words 3D moire is not visible to the observer.
Here, a triangular region formed by connecting the points A, B, and C and a triangular region formed by connecting the points A′, B′, and C′ of the display unit 4 are right triangles and situated within the overlapping region width Xct1. This is a crosstalk region where lights emitted from the right-eye pixel 4R and left-eye pixel 4L overlap with each other. The prior art pixel structure has to form at least such a crosstalk region to have a constant vertical aperture width in the X-axis direction, thereby causing 3D crosstalk (the rate of a right-eye or left-eye image leaking into the other) upon three-dimensional display.
Here, “3D moire” or “3D crosstalk” will be described in detail. In this specification, periodically appearing uneven luminance (sometimes referred to as uneven color) caused by displaying different images in different angular directions, particularly luminance angular fluctuation is defined as “3D moire.” On the other hand, the rate of a right-eye or left-eye image leaking into the other is defined as “3D crosstalk.”
Generally, fringes appearing when structures different in periodicity interfere with each other are called “moire fringes.” The moire fringes are interference fringes appearing depending on the periodicity or pitch of structures. The 3D moire is uneven luminance caused by the image-forming property of an image separation means. Therefore, the 3D moire is distinguished from the moire fringes in this specification.
The 3D moire may not be a problem in some observation positions. However, large luminance angular fluctuation presumably has some adverse effect on three-dimensional observation. Therefore, it is desirable that the magnitude of luminance fluctuation is equal to or lower than a given value.
On the other hand, a higher magnitude of 3D crosstalk may diminish three-dimensional effect and give the observer adverse effects such as tired eyes. Therefore, it is desirable that the magnitude of crosstalk is equal to or lower than a given value.
In this specification, with regard to the pixel shape shown in FIG. 36, the aperture ratio AP, 3D crosstalk 3Dct, and 3D moire 3Dmoire are defined as follows. From the pixel shown, the aperture ratio AP can be defined by the following formula from the area ratio between the shielding part and aperture.AP=Y1/(Y1+Y2+Y3)=(Ydot−Y3−Y2)/Ydot  [Math 1]
Furthermore, provided that 3D crosstalk contributes to a region as large as the sub-pixel pitch Xdot, 3D crosstalk (3Dct) can be defined by the following formula from the area ratio between the aperture region and overlapping region.3Dct=(Xct1×Y1)/(X1×Y1+Xct1×Y1)=Xct1/(X1+Xct1)=Xct1/Xdot  [Math 2]
Furthermore, 3D moire (3Dmoire) can be defined by the following formula from the ratio between the vertical aperture width Y1 in the non-overlapping region and the total of the vertical aperture widths of the right-eye and left-eye pixels 4R and 4L in the overlapping region.3Dmoire=1−(Y1+Y2−Wy)/Y1=(W/sin θ−Y2)/Y1  [Math 3]
Furthermore, in order to maintain the vertical aperture width constant in the X-axis direction, the following relationship must be established.Y2=W/sin θ  [Math 4]
Therefore, it is understood from the mathematical formulae 3 and 4 that the prior art pixel has ideally 3Dmoire=0 and there is no luminance angular fluctuation, whereby 3D moire is less visible.
However, it is understood from the mathematical formula 2 that the overlapping region width Xct1 is determined by the inclination θ of the oblique wire and 3D crosstalk (3Dct) is significant as the angle θ is increased.
In addition, in order to obtain a desired aperture ratio from the mathematical formulae 1 and 4, the inclination θ should be increased to a certain extent. For this reason, 3D crosstalk cannot be eliminated. Even if optical conditions for separating images are adjusted so that 3D crosstalk contributes to a region not larger than the sub-pixel pitch Xdot, 3D crosstalk cannot be eliminated either. In other words, the prior art pixel shown in FIG. 36 has a structure with low “3D moire” and high “3D crosstalk.”
By the way, the display panel of a display apparatus is required to have a smaller pixel pitch in order to improve the fineness and have a higher so-called aperture ratio determined by the area ratio between the aperture and shielding part and contributing to the display luminance in order to improve the display luminance. This also applies to a three-dimensional display apparatus.
However, for a finer image, one pixel has to be made much smaller because many pixels have to be arranged in a screen region, which is small from the beginning. In other words, how much the pixel size can be reduced is an issue.
As semiconductor microscopic processing techniques advance, smaller pixels have been realized. However, electric/electronic circuits such as switching elements and auxiliary capacitors driving the liquid crystal for modulating light may not always be downsized in proportion to much finer pixels. This is because the switching elements and auxiliary capacitors are created on a semiconductor or glass substrate using microscopic processing techniques and the limitation of semiconductor process imposes an upper limit on the realizable fine line width. Even if finer processing is technically available, investment in equipment will be costly at least for the present.
Furthermore, a liquid crystal display apparatus undergoes increase in the shielding region, namely decrease in the aperture ratio, because of limitation accompanying higher fineness, having a problem that the display apparatus overall uses light less efficiently. In other words, improving the image quality by finer pixels leads to less efficient use of light. Therefore, it is an issue with a liquid crystal display apparatus to realize a finer image and realize a high quality and highly efficient image display apparatus.
A three-dimensional display panel having two or more observing points as in the three-dimensional image display apparatuses disclosed in the Patent Literature 1 and 2 has multiple sub-pixels corresponding to the number of observing points in one pixel. Therefore, the area involved in wires and switching elements in one pixel is increased. Particularly, a finer pixel has a significantly decreased aperture ratio and therefore, improvement in the aperture ratio is an important issue.
For the above reason, a finer pixel has to be designed with priority at least on the aperture ratio in order to ensure a desired transmittance. In order to increase the aperture area, the wire angle θ in the boundary region must be increased. However, if the wire angle θ is increased, the overlapping region width Xct1 is also increased, whereby 3D crosstalk becomes so significant that the visibility of three-dimensional display is adversely affected. Particularly, as disclosed in the Patent Literature 1, when a square pixel is divided in the vertical direction according to the number of observing points and color filters are provided in a horizontal stripe pattern, a sub-pixel becomes very small in the Y-axis direction depending on the number of colors. As a sub-pixel becomes small in the Y-axis direction, because the oblique wire has a finite width, the vertical aperture width in the X-axis direction cannot be maintained constant even if the inclination θ is increased. In other words, it is difficult to realize a fine pixel structure ensuring both 3D crosstalk and the aperture ratio and having a nearly constant vertical aperture ratio for reducing 3D moire.
On the other hand, in a three-dimensional display system using a lenticular lens to separate images, the spot diameter should be reduced to improve the separation performance of the lens in order to increase the region in which a three-dimensional image is comfortably observed. Recently, advanced lens processing techniques allow for application of lenses having a spot diameter in the order of several microns. However, as the spot diameter is reduced, slight geometric change due to the processing accuracy of production process is augmented even in a pixel structure designed to have a nearly constant vertical aperture width in the image separation direction as in the prior art technology shown in FIG. 36. Consequently, uneven luminance locally occurs, significantly deteriorating the image quality.
In the above explanation, a sub-pixel has an isosceles trapezoid aperture. It is obvious that the near parallelogram pixel structure disclosed in the Patent Literature 2 has the same problems.
The present invention is invented in view of the above circumstances and an exemplary object of the present invention is to provide an image display apparatus having 3D crosstalk reduced and the aperture ratio improved while minimizing the influence of 3D moire so as to improve the three-dimensional display quality.